Transcutaneous electrical nerve stimulation (TENS) is a non-invasive technique in which a low-voltage electrical current is delivered through wires from a small power unit to electrodes located on the skin. Electrodes are temporarily attached with paste in various patterns, depending on the specific condition and treatment goals. TENS is often used to treat pain, as an alternative or addition to pain medications. Therapy sessions may last from minutes to hours. TENS devices can be set in a wide range of frequencies and intensities, depending on patient preferences, desired sensations, and treatment goals. "Conventional TENS" involves the delivery of high or low frequency electrical current to affected areas. In "acupuncture-like TENS," lower frequencies are used at specific "acupuncture points" or trigger points. TENS may also be applied to locations on the ear ("auricular points"). Epidural stimulation and percutaneous electrical nerve stimulation (PENS), which are not included in this review, are invasive procedures that require penetration of the skin, implantation, or minor surgery. The practice of using electricity for pain control can be traced to 2500 BC and the Egyptian Fifth Dynasty, in which stone carvings depict an electric fish being used to treat pain. During the Socratic era, electrogenic torpedo fish ( Scribonius longus ) were used to treat arthritis and headache. In the Middle Ages, electrostatic generators were used, and the discovery of the electric battery in the 19th century led to further experimentation. The use of electrical stimuli for pain relief was popularized in the 19th century and became widespread in the 1960s and 1970s using battery power.
The practice of acupuncture originated in China 5,000 years ago. Today it is widely used throughout the world and is one of the main pillars of Chinese medicine. There are many different varieties of the practice of acupuncture, both in the Orient and in the West. The most common forms available to westerners are as follows. Traditional Chinese medicine (TCM) usually combines acupuncture with Chinese herbs. Classical acupuncture (also known as five element acupuncture) uses a different needling technique and relies on acupuncture independent of the use of herbs. Japanese acupuncture uses smaller needles than the other varieties. Medical acupuncture refers to acupuncture practiced by a conventional medical doctor. Auricular acupuncture treats the entire body through acupuncture points in the ears only. Electroacupuncture uses electrical currents attached to acupuncture needles. Aside from needles, other methods of stimulation are also considered forms of "acupuncture." These include the use of heat from the burning of herbs placed on specific points ("moxibustion") and the placement of herbal pastes on specific points. Research on the effectiveness of acupuncture has special challenges. These include the diversity of approaches, the practice of individualizing treatment for each patient, differing skill levels between practitioners, and difficulty separating out the effects of acupuncture from placebo effects (i.e., how the patient's beliefs and expectations affect his/her perception of symptoms). Based on acupuncture's long history of use as well as the limited research available, both the World Health Organization and the National Institutes of Health have identified many conditions for which it may be recommended. However, many common uses do not yet have formal scientific evidence to support them.